Lubrication

SAF and SAW pillow (plummer) blocks can accommodate grease, oil bath or circulating oil lubrication systems. Any sealing solution can be used with grease lubrication, while for oil lubrication SKF does not recommend using labyrinth rings in the LER series.

The lubricant should be selected based on the operating conditions of the bearing. For additional information, refer to Lubricant selection.

Initial grease fill

If no other requirements exist, the free space in the bearing should be completely filled with grease and the free space in the housing should be filled to 20 to 40% of its volume. A 40% grease fill is required when bearings have to be relubricated from the side, while a 20% grease fill is used when bearings are relubricated via the outer ring.

For highly contaminated environments and slow speeds, fill the housing to 70 to 80%. For best protection against contaminants, use the SKF Three-Barrier Solution. For additional information, contact the SKF application engineering service.

Quantities for 20% and 40% grease fills are listed in table 1 and table 2. The values are valid for a typical lithium grease (about 0.57 oz/in3). The grease to fill labyrinth seals or taconite heavy-duty seals is not included. For sealed bearings, the values have to be adjusted.

In most applications, the initial grease fill will adequately lubricate the bearing until the grease is exchanged during the next planned maintenance interval.

Relubrication

SAF and SAW housing caps have two drilled and tapped lubrication holes, one centred and one offset (fig. 1) that are sealed with standard pipe plugs.

The housings also have dimples on the cap where holes can be drilled and tapped if other positions are required. Two dimples on the outer sides of the central ridge indicate the position of lubrication holes to lubricate labyrinth seals. All SAF and SAW housing bases are equipped with a drain plug on each side (fig. 2) to purge or drain old lubricants or to serve as an outlet for circulating oil. The sump in the housing base is large enough to accommodate a sufficient quantity of lubricant to provide reliable long-term operation.

The hole in the centre of the cap should be used to relubricate spherical roller bearings with a relubrication feature (a lubrication groove and holes in the outer ring) (fig. 3). When applying grease via the relubrication feature, the shaft should be rotating.

Narrow bearings (dimension series 13 and 22) in the locating position can be displaced axially, so that the relubrication groove in the bearing does not line up with the relubrication hole in the housing cap. Make sure the bearing is sufficiently centred when relubricating.

Oil bath lubrication

The level of oil should be at about the centre of the lowermost rolling element when the bearing is stationary. Values for the oil level are listed in table 3 and table 4. For higher speeds, the level should be slightly lower to reduce the effects of lubricant churning – about 1/8 in. above the corner of the outer ring raceway of the bearing. For additional information contact the SKF application engineering service.

An oil sight glass should be used to monitor the oil level during operation. It can be mounted to one of the drain holes in the housing base. The static oil level should be marked on the sight glass during installation and a running level should be marked immediately after start-up. Depending on the type of bearing and the speed and direction of rotation, the running level will either rise or fall from the static level.

Circulating oil lubrication systems

When using a circulating oil lubrication system with SAF and SAW pillow blocks, oil is introduced through one of the inlet holes in the housing cap and drained from one or both holes in the base. For spherical roller bearings, oil should be introduced through the centre hole in the cap and drained from both sides of the base (fig. 5). For self-aligning ball bearings and CARB toroidal roller bearings, oil should be introduced through the offset hole in the cap and drained from the opposite side of the base so that oil is forced through the bearing (fig. 6).

Drains should lead downward immediately outside of the housing to prevent the accumulation of oil in the housing. Too high an oil level can result in higher operating temperatures due to churning of the lubricant. The drain piping must be adequately sized and arranged to provide adequate drainage. Additional considerations may be necessary when using circulating oil. These can include special seals, cross drillings in the housing, wet sump requirements, flow rates, and enlarged drain holes. For additional information, contact the SKF application engineering service.